1. Field of the Invention
The present invention relates to detecting events. More particularly, the present invention relates to sampling nuclear radiation detector signal outputs representing events.
2. Discussion of Background
There exist many devices and techniques for obtaining event data from detectors. Many detectors are used for detecting radiation pulse charges or other radiation events, and have been connected to detection systems that are, for the most part, analog in nature.
For example, radiation detectors are used in U.S. Pat. No. 5,132,540, by Adolph et al, which features nuclear spectroscopy analysis device for detecting random nuclear events, and in U.S. Pat. No. 4,599,690, by Stoub. Also, Inbar et al, in U.S. Pat. No. 4,369,495 and Thompson et al, in U.S. Pat. No. 4,228,512, disclose radiation charge detectors.
Usually, collection systems for such detectors are event-triggered, that is, when the detector output exceeds a certain threshold value, the collection system enables the data collection or other processing devices. The data stream present at that time is collected or processed until the detected value falls below the threshold value, whereby the device is returned to its normal or "non-event" state.
An event-triggered system has several limitations, one of which is known as dead-time. Due to the nature of the event-triggered system, once the system is triggered by the start of an event, the system cannot collect or otherwise process subsequent data until returned to its normal or "non-event" state at the conclusion of the first event.
This time interval, during the collection and processing of the first event data, is called dead-time, since the system is essentially oblivious to any incoming signals of subsequent events until the prior event is processed. Dead-time limitations can be attributed to the collective speed of the individual component devices of the system in relation to the frequency of event occurrence and detection. Also, storage and processing time in relation to the frequency of data collection contributes to dead-time.
Another problem with event-triggered systems is distinguishing between separate, nearly simultaneous, detected events. Because the event-triggered system is enabled when a detected signal is above a threshold value and disabled when a detected signal is below the threshold value, the nearly simultaneous occurrence of more than one event is often treated by the system as a single event of extended duration.
This lack of discrimination occurs because the later event begins and is detected above the threshold value before the former event is completed and the system can return to its normal state from the first event. Consequently, the signals of the two separate events are not resolved by the system but are treated as a single event.
Obviously, the limitations of event-triggered systems lead to inaccurate collection, storage and processing of event data. As a result, some or even all of the data has to be discarded or data lost during the system dead-time may have to be synthesized by statistical or other compensation methods.
For instance, Adolph et al, in U.S. Pat. No. 5,132,540, uses comparative reference data to determine data undetected because of dead-time. In U.S. Pat. No. 4,599,690, Stoub corrects for dead-time using a replication probability. Similarly, Inbar et al, in U.S. Pat. No. 4,369,495, uses synthetic pulses based on a statistical correction factor. However, these compensating methods are often inadequate for replacing information undetected because of dead-time and processing delays.
There exists a need for a sampling, collection, and processing system that records substantially each event.